Sampling the complete organ instead of defined parts might affect analysis at both the cellular and transcriptional levels. We defined host responses to H9N2 avian influenza virus (AIV) in trachea and different parts of the lung. Chickens were spray-inoculated with either saline or H9N2 AIV. Trachea and lung were sampled at 1 and 3 days post-inoculation (p.i.) for immunocytochemistry, real-time quantitative RT-PCR and gene-expression profiling. The trachea was divided into upper and lower parts and the lung into four segments, according to anatomy and airflow. Two segments contained the primary and secondary bronchi, cranial versus caudal (parts L1 and L3), and two segments contained the tertiary bronchi, cranial versus caudal (parts L2 and L4). Between the upper and lower trachea in both control and infected birds, minor differences in gene expression and host responses were found. In the lung of control birds, differences in anatomy were reflected in gene expression, and in the lung of infected birds, virus deposition enhanced the differences in gene expression. Differential gene expression in trachea and lung suggested common responses to a wide range of agents and site-specific responses. In trachea, site-specific responses were related to heat shock and lysozyme activity. In lung L1, which contained most virus, site-specific responses were related to genes involved in innate responses, interleukin activity and endocytosis. Our study indicates that the anatomy of the chicken lung must be taken into account when investigating in vivo responses to respiratory virus infections.

Infection of chickens with low pathogenicity avian influenza (LPAI) virus results in mild clinical signs while infection with highly pathogenic avian influenza (HPAI) viruses causes death of the birds within 36–48 hours. Since natural killer (NK) cells have been shown to play an important role in influenza-specific immunity, we hypothesise that NK cells are involved in this difference in pathogenicity. To investigate this, the role of chicken NK-cells in LPAI virus infection was studied. Next activation of lung NK cells upon HPAI virus infection was analysed. Infection with a H9N2 LPAI virus resulted in the presence of viral RNA in the lungs which coincided with enhanced activation of lung NK cells. The presence of H5N1 viruses, measured by detection of viral RNA, did not induce activation of lung NK cells. This suggests that decreased NK-cell activation may be one of the mechanisms associated with the enhanced pathogenicity of H5N1 viruses.

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Natural killer (NK) cells are cytotoxic lymphocytes and play an important role in the early defence against viruses. In this study we focussed on NK cell and interferon (IFN) responses after infection with infectious bronchitis virus (IBV). Based on surface expression of CD107+, enhanced activation of lung NK cells was observed at 1 dpi, whereas in blood prolonged NK-cell activation was found. IFN-α and IFN-β mRNA and proteins were not rapidly induced whereas IFN-γ production in lung, measured by Elispot assay, increased over time at 2 and 4 dpi. In contrast, IFN-γ production in blood was highest at 1 dpi and decreased over time down to levels comparable to uninfected birds at 4 dpi. Collectively, infection with IBV-M41 resulted in activation of NK cells in the lung and blood and rapid production of IFN-γ and not IFN-α and IFN-β compared to uninfected birds.

increase in IL-2Rα + NK cells and enhanced NK cell activation. The observed association between early life development of intestinal microbiota and immune system indicates possibilities to apply microbiota-targeted strategies that can accelerate maturation of intestinal microbiota and strengthen the immune system, thereby improving the health and resilience of broiler chickens.